1. Field of Invention
This invention pertains generally to the field of lens fabrication and more particularly to inspecting and processing a lens during manufacture.
2. Description of Prior Art
The fabrication of lenses includes processing steps to generate both lens surfaces in order to impart specific optical properties to the lens, and also to accomplish the peripheral alteration, or edging, of the lenses. The first step in altering a lens is typically the generation of a surface on a partially finished lens blank. The second step in processing the lens is normally the peripheral alteration of the shape of the surfaced lens. The lens blanks and surfaced lenses may be, for example, spherical, cylindrical, optical flats, aspherical, or of multiple focal lengths. Once the lenses have been finished they may be put to a variety of uses such as spectacle lenses, camera lenses, or lenses used in instrumentation.
Edging the lens to obtain a desired shape involves a series of steps. Typically the optical center and the cylinder axis of the lens is located and marked on a surface. Next the lens is attached to a lens block by some type of holding mechanism, such as an adhesive, so that the optical center and the cylinder axis of the lens are aligned with the center point and cylinder axis of the block. The desired peripheral shape is then imparted to the lens via one or more drilling, cutting, milling, grinding or other machining tools.
Typically the lens cutting and shaping tool is a computer controlled programmable device that may be frequently reprogrammed to manufacture a wide variety of lenses. In order to verify proper programming and operation of the lens forming tool, some means of calibration must be provided.
For example, U.S. Pat. No. 7,191,030, entitled “METHOD FOR ESTIMATING THE ANGULAR OFFSET, METHOD FOR CALIBRATING A GRINDING MACHINE FOR OPTHALMIC GLASSES AND DEVICE FOR CARRYING OUT SAID CALIBRATING METHOD” utilizes a reference standard lens of a predetermined known shape.
U.S. Pat. No. 7,668,617 entitled “METHOD OF CALIBRATING AN OPTHALMIC LENS PIERCING MACHINE, DEVICE USED TO IMPLEMENT ONE SUCH METHOD AND OPTHALMIC LENS MACHINING APPARATUS COMPRISING ONE SUCH DEVICE”, uses a template marked with an associated coordinate system. An additional drilling calibration device is used to calculate the difference between the apparent markings on the template and the actual drilling angles needed to create the desired lens.
U.S. Pat. No. 7,970,847 entitled “METHOD OF CALIBRATING AN OPTHALMIC LENS PROCESSING DEVICE, MACHINE PROGRAMMED THEREFOR, AND COMPUTER PROGRAM”, presents a scheme for comparing the number of holes actually drilled in a lens with the number of holes predicted according to the programming of a drilling device.
Further, some means must be provided to attach the lens blank to the edging block with a bond that will not fail during alteration but that will permit removal once alteration is complete. In practice, the lens may be removed from the edging block by a variety of methods. For example, the lens may be pried from the block. However, this method has the disadvantage that the lens is often chipped, scratched, or otherwise damaged by the act of prying. This method can be facilitated by immersing the lens and block in hot water for a short period of time. However, some plastic lens materials cannot withstand such temperatures.
Another method of lens removal employs a tab that is pulled in the direction of the plane of the blocking pad so as to cause a reduction in the thickness of the pad and a progressive disengagement of the pad from the interface between lens and block. Removal may also be accomplished by placing the combination of lens, blocking pad and block into a cavity of the mounting block and then rotating the lens and the block in opposite directions with respect to each other, thereby causing them to separate. A specially designed hand tool may also be provided to accomplish this same result. The tool is not as wide as the mounting block and facilitates removal by making it easier to grasp the edge of the lens.
The latter method of lens removal is disclosed in U.S. Pat. No. 3,962,833 entitled METHOD FOR THE ALTERATION OF A LENS AND AN ADHESIVE LENS BLOCKING PAD USED THEREIN, issued to Johnson on Jun. 15, 1976. The problem with the lens removal method disclosed by Johnson is that an operator must manually and repeatedly grasp pliers or a similar tool to remove the lens. Some level of skill is required to perform the lens removal operation rapidly while avoiding damage to the lens. After a period of time in such an occupation, the operator is likely to suffer various forms of fatigue and injury including, for example, carpal tunnel syndrome.
Another method of lens removal utilizes a device that retains the blocked lens by means of a collet chuck or clamp. An example of such a device is disclosed in U.S. Pat. No. 8,182,314 entitled AUTOMATED EDGED LENS DEBLOCKING SYSTEM, issued to Goerges on May 22, 2012. The blocked lens resides on a pad which supports the lens on the edging block while protecting the lens from abrasion or damage from the block itself. A pair of opposed movable lens clamps or arms are pneumatically advanced to grip the blocked lens along portions of the lens edge. Once the lens is secured by the lens clamp, the collet chuck is rotated approximately forty five degrees, thereby breaking the bond between the lens and the edging block. The lens clamps may then be retracted away from the lens edges and the lens may be manually removed from the pad.
A problem with the geometry of the '314 device is that repeated use causes wear on the collet chuck that leads to relatively premature failure, particularly when a hydrophobic adhesive pad is applied to an uncoated lens. Use of the hydrophobic pad requires a substantially greater force for lens removal than other pad/lens combinations, thereby accelerating the wear on both the collet and the edge block.
What is needed is a visually verifiable lens template that permits a wide variety of lens parameters to be immediately inspected after a lens machining tool is programmed to create a specific lens. Any error or anomaly in the lens created, and the nature of the corrective action needed, should be apparent by viewing the lens template without further need of a machine based analysis. Further, the edged lens deblocking device must be capable of repeated industrial scale operation without failure.